CRT in RBBB — EECC MCQ

Correct answer: E — CRT may be considered (Class IIa for ≥150 ms, Class IIb for 130-149 ms) but evidence in RBBB is weaker than in LBBB — RBBB indicates RV conduction delay which LV-based CRT does not correct; response rates are lower (~30-40% vs ~70% for LBBB)

The CRT evidence base is primarily built on LBBB patients (COMPANION, CARE-HF, MADIT-CRT, RAFT trials predominantly enrolled LBBB). In RBBB: (1) the conduction delay is primarily in the RV, not the LV — LV-based CRT (pacing the LV via CS lead) does not correct RV dyssynchrony; (2) echocardiographic mechanical dyssynchrony may not be present in RBBB the way it is in LBBB; (3) response rates are substantially lower (~30-40%). The ESC 2021 Pacing/CRT Guidelines reflect this: RBBB + QRS ≥150 ms = Class IIa (lower evidence grade); RBBB + QRS 130-149 ms = Class IIb. Subgroup analyses of CRT trials show inconsistent benefit in RBBB. Some experts suggest considering His bundle pacing or LBBAP for RBBB patients, as conduction system pacing may correct the RV delay more physiologically.

Reference: ESC (2021): Pacing/CRT Guidelines